I'm currently working on a stripped-down purpose-built custom desktop environment on top of Ubuntu. For most of the major Desktop Environments including GNOME or any DE you install after the fact (KDE, XFCE, etc...), they are added automatically to the list of available, optionable desktop environments for X11 when they're installed.

How would one go about manually adding a DE boot option for the list of available DE's in Ubuntu 12.10 or another version. I'm assuming this is part of the X11 config somewhere but i"m not seeing anything that is immediately apparent as the location for storing the available options...

I'd like to have to option to switch back to GNOME while I debug while developing the new DE so that I can actively develop it in GNOME, build, log off, choose my newly built DE as the DE to log into to test, etc...